Israeli anti-spam firm Blue Security Tuesday said that it is ceasing operations after a crippling series of attacks launched against its services earlier this month by a Russian spammer named PharmaMaster.

The episode serves as an alarming reminder of the challenges involved in dealing with spammers and the resources they have at their disposal to deter those trying to stop them, analyst said.

In a statement Tuesday, Blue Security, which has its U.S. headquarters in Meno Park Calif., said it can no longer "take the responsibility for an ever-escalating cyber war through our continued operations.

"As we cannot build the Blue Security business on the foundation we originally envisioned, we are discontinuing all of our anti-spam activities on your behalf and are exploring other, non-spam-related avenues for our technological developments," the company said.

The decision comes only days after Blue Security re-started operations following a massive and sustained denial of service (DoS) attack launched against it by PharmaMaster earlier this month.

Blue Security operated a fairly controversial anti-spam service designed to deter junk-mailers by spamming them back. Blue Security's Do Not Intrude program allowed individuals to register their e-mail addresses with the company and essentially flood spammers who sent them e-mail with automated opt-out requests.

Since the free service was launched on a trial basis last summer, Blue Security claimed to have signed up more than 500,000 subscribers -- including corporate customers -- and had gotten six out of the top 10 spammers to abide with their opt-out lists.

But the speed at which the company folded following the DoS attacks suggests that it was ill-prepared to deal with the consequences of attacking spammers directly, said Todd Underwood, chief operations and security officer at Renesys, a Manchester, N.H.-based Internet monitoring company.

"Spammers have a history of launching massive attacks against those who try to stop them," Underwood said. While others have taken precautions against such attacks by building more redundancy into their networks, Blue Security appears to have been "woefully under-prepared for the things that happen when you attack spammers," he said.

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